APS are solid state imagers where each pixel contains a photo-sensing means, reset means, charge to voltage conversion means, and all or part of an amplifier. APS devices have been operated in a manner where each line or row of the imager is selected and then read out using a column select signal (analogous to a word and bit line in memory devices respectively). The row select operation has been accomplished in prior art devices by incorporation of a row select transistor in each pixel that is turned on to make that row active (see FIG. 1). Since this transistor is placed in each pixel, its inclusion reduces the fill factor for the pixel because it takes up area that could otherwise be used for the photodetector, or charge storage region. This reduces the sensitivity and saturation signal of the sensor.
In order to build high resolution, small pixel APS devices, it is necessary to use sub-micron CMOS processes in order to minimize the area of the pixel allocated to the row select transistor and other parts of the amplifier in the pixel. In essence, it takes a more technologically advanced and more costly process to realize the same resolution and sensitivity APS device compared to a standard charge coupled device (CCD) sensor. However, APS devices have the advantages of single 5V supply operation, lower power consumption, x-y addressability, image windowing, and the ability to effectively integrate signal processing electronics on-chip, when compared to CCD sensors.
One approach to providing an image sensor with the sensitivity of a CCD and the advantages of an APS device, is to improve the fill factor and sensitivity of an APS device. This present invention addresses these problems that exist within the prior art by simplifying the circuitry used in addressing the imager.